In our Australian Patent 534452 entitled "Improvements in Pipe Fittings", a pipe fitting was described and illustrated wherein a sleeve was provided with a tail for insertion into a pipe, and there was also provided a compression ring having serrations thereon for compressing the end of the pipe against the outer surface of the tail, the tail preferably having serrations thereon. There was also provided a sealing ring of elastomeric material which engaged between the sleeve and a body, and the assembly was achieved by means of a sleeve nut which had a tapered inner surface which engaged a complementary male tapered outer surface of the compression ring. The sleeve was also provided with a pair of spaced peripheral flanges, one bearing against the resilient gasket ring and the other bearing against one end of the compression ring, so that the axial distance between those two rings did not vary upon tightening of the nut.
The pipe fittings described in the aforesaid specification have proven to be very successful, both technically and commercially. Failure is almost unknown and in some areas of the world fittings made in accordance with that specification are sold in greater numbers than their competitor's fittings.
A practical problem which is frequently encountered with fittings made in accordance with said patent 534452 (and other fittings in common use), is that the nut and compression ring needs to be positioned over a pipe end before tail of the sleeve is inserted. If either the nut or ring is inadvertently omitted, the tail usually cannot be withdrawn (because of barbed serrations), and it becomes necessary to cut the pipe.
The main object of this invention is therefore to provide improvements whereby the body, nut and gripping member (compression ring) can comprise a preliminary assembly through which can be inserted a pipe, which can simply be secured by tightening the nut, or removed by unscrewing.
Further, there is a need for a fitting which does not always have a tail inserted within a pipe, thereby avoiding interference with fluid flow within the pipe, and which takes advantage of the existence of an acceptable standard of accuracy of diameter of some polymeric pipes. For example the variation in outer diameter of a 50 mm pipe is likely to be less than 0.5 mm (0.020"). This makes it possible to have a coupling which engages only the outer surface of a pipe, and which restrains a pipe against leakage and against axial displacement, relying upon the stiffness of the pipe itself.
It is known that there exist fittings each comprising an outer cylindrical body which does not have any sleeve nut, but has an inner taper surface which converges in the direction of the pipe to which it is to be attached, the inner taper surface co-operating with a compression sleeve having a sawtooth profile to grip the outer surface of a pipe, and the pipe is merely pushed into the end of the body and through the taper sleeve and pulled outwardly again, causing the sawtooth projections to firmly grip the surface of the pipe, and retain the pipe in position. This is a simple and inexpensive fitting, but sometimes disassembly is difficult to achieve.
In some prior art fittings, it is sometimes necessary to chamfer a pipe end before insertion into the fitting, or lubricate a pipe end, or both, and this is quite inconvenient. Further, manual insertion is sometimes necessary to effect a seal between pipe and fitting, and this can involve distortion of a gasket ring, by application of direct axial force.
Another of the objects of this invention is to provide a coupling which comprises a nut which positively both compresses a gasket ring against a surface to effect a seal against leakage, and which limits the amount of gripping of the pipe, both to a predetermined level, thereby providing means which prevents excessive distortion of the resilient gasket ring, and also controls the degree of compression of a gripping member onto a pipe. Without such limiting means, a possibility exists of destruction of the split ring. It is known in the art that split rings of the "finger" type can be destroyed upon excessive forces being imparted.
A further difficulty which may conceivably be encountered with fittings of the sleeve type which contain both resilient gaskets and split rings with sawtooth profiles, is that although supplied in relaxed state, they can be tightened by hand inadvertently and thereby force the resilient gasket ring into a tapered socket from which it is not readily withdrawn. Such fittings if again relaxed, leave the gasket rings in position and there is always a danger of damage with consequential subsequent leakage if the gasket rings are hooked out or pushed out with a sharp instrument. A further object of the invention is to provide means whereby the resilient gasket ring will be withdrawn upon unscrewing of the nut.
A still further object of the invention is to have an arrangement whereby the degree of compression of the resilient gasket ring and gripping member with inwardly directed barb projections is controlled by the dimensions of the components of the coupling to be effective within a range of tolerance of diameter of the pipe with which the coupling is to be used, ensuring proper sealing of the resilient gasket ring and proper gripping of the pipe even when the pipe is on "bottom tolerance", but also assuring that there is unlikely to be damage to the resilient gasket ring, to the gripping member or to the pipe due to over tightening of a sleeve nut.
Situations arise whereby pipes produced to different standards (Australian, I.S.O., British, American etc) vary by relatively small amounts in their bore, but the outer diameters are not always compatible with a fitting made to a different standard, and a still further object of the invention is to provide a transition means between a pipe and a fitting, so as to reduce inventory costs, one standard size fitting then being useable with pipes of similar but not identical size made to different standards by a mere selection of inexpensive transition means.